Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$133.44	4.715%	$139.7317	$139.73	$139.75	$139.70
Purchase #2	$62.34	3.424%	$64.4745	$64.47	$64.45	$64.50
Purchase #3	$245.70	13.610%	$279.1398	$279.14	$279.15	$279.10
Purchase #4	$118.27	8.584%	$128.4223	$128.42	$128.40	$128.40
Purchase #5	$100.81	10.565%	$111.4606	$111.46	$111.45	$111.50
Purchase #6	$127.71	9.388%	$139.6994	$139.70	$139.70	$139.70
Purchase #7	$141.46	9.703%	$155.1859	$155.19	$155.20	$155.20
7 purchase totals =	$929.73		$1,018.1142	$1,018.11	$1,018.10	$1,018.10